In this post, I am particularly referring to a major scale, which most songs are played in. You know when you hear someone saying "This song is played in G", it kind of means that it is using a G major scale. Before I start explaining, bear in mind that this has to do with music theory (which I am currently trying to improve on), so it might be a little dry. However, I'll try to explain it the best I can.
I'm pretty sure you have heard people singing "Do-Re-Mi-Fa-So-La-Ti-Do" before right? Believe it or not, that is actually a major scale. So, if you want to play a C major scale, you start with a C note (that will be your "Do"). The next step is to just play the rest of the "Do-Re-Mi-Fa-So-La-Ti-Do" sounds, and you would have played a C major scale.
That is my attempt of explaining what a major scale is in lay-man terms. However, there is music theory behind this. The formula for a major scale is : 1 1 ½ 1 1 1 ½. What does the 1s and ½s mean? Well, they refer to tones and semi-tones. "1" is a tone, and "½" is a semi-tone. 1 tone is 2 notes apart, and ½ tone is 1 note apart. So, a C to D is a tone because there is a C# in-between. From B to C is a semi-tone because there is no B# in between etc.
I will write out the C major scale (notice the letters in bold, they are the notes that are in the C major scale):
1 1 ½ 1 1 1 ½C C# D D# E F F# G G# A A# B C = C D E F G A B C
Notice how the formula 1 1 ½ 1 1 1 ½ is applied? So, technically, if I play a song in C and use any of the notes in bold from above, the song will sound pretty alright because those notes lie within the C major scale. This is especially good for guitarists who want to play melodies to a song, or even guitar solos etc.
Anyway, let me try to explain step by step how you can figure out the major scale. Let's try a D major scale.
First step is to just write out all the notes in order starting from the note that you are writing your scale in. In this case, it is a D.
D D# E F F# G G# A A# B C C# D
Second step is to apply the formula "1 1 ½ 1 1 1 ½" to the notes that you have written out
1 1 ½ 1 1 1 ½D D# E F F# G G# A A# B C C# D = D E F# G A B C# D
There you go. So, the D major scale is D,E,F#,G,A,B,C#, D. Try hitting those notes on your guitar (in the order above), it will give you the "Do-Re-Mi-Fa-So-La-Ti-Do" sound. I hope this is pretty interesting to you.
Let's try one more example to see if you understood what I was saying. Let's try an E major scale.
Apply the first step (write out all the notes, starting with the E note)
E F F# G G# A A# B C C# D D# E
Apply the second step (apply the formula)
1 1 ½ 1 1 1 ½E F F# G G# A A# B C C# D D# E = E F# G# A B C# D# E
Are you getting the hang of it? You can now try for other keys. Like F, G and A. If you want to challenge yourself a little, try with the harder keys like C#, D#, F#, G# and A#.
If you have any problems, do let me know. I hope you have fun practicing your theory =) Perhaps in my next post, I'll attempt to explain how chords are formed (it is really just playing certain notes together). Till then, please try to write out the major scales for C, C#, D, D#, E, F, F#, G, G#, A, A# and B